There are several methods to extract three-dimensional (3D) information out of collections of two-dimensional (2D) transmission electron micrographs. These include stereograms, weighted back projection (WBP), and simultaneous iterative reconstruction technique (SIRT) methods. There are several applications for extracting the third dimension from transmission electron micrographs, some of which are 3D characterization of dislocations, second phases and irradiation defects. One of the limitations to using weighted back projection or SIRT, is that the quality of the tomogram is related to the range of the tilt and the tilt increment between images. Larger tilt ranges and smaller tilt increments produce higher quality tomograms. Acquiring a series of images with a 70° tilt range with 1° tilt increments, which is typical, limits the application of the technique due to the time-consuming nature.
There are methods employed to reduce the number of images required to produce a tomogram using WBP or SIRT. For example, fiducial markers may be placed on the image at positions of features (for example, where the dislocations end at the surfaces of the foil) which aids the alignment of the images in the reconstruction software. By using this method, tomograms may be constructed using as few as 15 images and have enabled tomograms to be constructed at several stages during an in situ straining experiment in 304 stainless steel.
Even at 15 images, the acquisition process is time consuming. Another significant drawback to conventional electron tomographic methods during in situ straining experiments is that the image contrast should be held constant through the series of images acquired and deviations in contrast such as those found in images near a zone-axis in crystalline samples should not be used. In situ strain transmission electron microscopy (TEM) stages almost exclusively have a single axis of specimen tilt with few exceptions, maintaining the same imaging conditions in crystalline samples for a necessary range of tilt is not likely.
Stereomicroscopy for TEM gets around the necessity of acquiring tens of images, and instead uses 2 images. Interpretation is done by creating an anaglyph or using a stereoviewer, which still requires the two images to be at the same diffraction conditions if the sample is crystalline. Extracting the 3D information is possible using the basis behind stereomicroscopy, the parallax, however, the process previously was tedious.
Accordingly, an improved 3D visualization software method may be beneficial.